1. Field of the Invention
The present invention relates generally to a diode laser and, more specifically, to a strip-shaped semiconductor laser diode having a discontinuity structure, such as a grating for monomode-stabilization.
2. Description of the Prior Art
Laser diodes having a double hetero-structure are known. For instance, Amann U.S. Pat. No. 4,352,187 discloses a semiconductor laser diode having an electrode on a strip-shaped highly doped layer overlying a lesser doped layer. A metal clad ridge waveguide is thus formed wherein the highly doped layer forms a low resistance junction to restrict the current path to a strip-shaped area thereby forming a strip-shaped laser-active zone.
To obtain improved monomode, or single mode, laser radiation, numerous proposals have been made for laser diodes. One approach is to provide a plurality of coupled laser-active zones disposed parallel to one another in a laser diode. A second approach is to provide a so-called "grating" within the double hetero-layer structure at the laser active zone. A grating is a geometrical structure with discontinuities arranged transversely relative to the direction of the laser radiation. The discontinuities are distributed periodically, at least to a certain degree, in a longitudinal direction of the laser radiation to provide periodic variation of the refractive index and thus effect the laser radiation. The use of gratings is disclosed in 9 IEEE Journal of Quantum Electronics No. 9, pages 919-933 (September 1973) and 11 IEEE Journal of Quantum Electronics No. 11, pages 867-873 (November 1975).
The manufacturing of such a grating within the double hetero-layer structure, and particularly within the resonant zone, means that an interruption must occur in the epitaxial manufacturing methods of the double hetero-layer device. After the deposition of the first layers of the double hetero-layer structure on a substrate, the epitaxial deposition must be interrupted, the grating produced, and only then can deposition of the further layers be continued. During such interruption, the substrate body of the device must be removed from the epitaxy apparatus. There are numerous disadvantages in such a procedure which relate to the quality of the double hetero-layer structure formed thereby and to the considerable additional technological outlay associated with continuing the layer formation.
It would therefore be an advantage over the devices of the prior art to form a grating or discontinuity structure in a hetero-layer structure laser diode in a simple, uninterrupted manufacturing process.